Humidifier

An HVAC humidifier is a device or system that is used to add moisture to the air in a home or other environment. The device works by taking in dry air from the environment and passing it over a wet surface or through a spray of water. The water evaporates into the air and increases the humidity of the air in the environment. This is beneficial for many reasons, including increasing the comfort of the occupants, reducing dust and allergens in the air, and helping to protect wood furniture and floors from cracking or warping due to dry air. Additionally, a properly functioning HVAC humidifier can help reduce energy costs as it allows the HVAC system to operate more efficiently.

When the condition of the air entering a spray washer is humid, it can be expected to be humidified. However, if the spray is cooler than the air and the dew point, the vapour pressure of the spray will be lower than that of the moisture in the air and some moisture will be transferred into the spray water – resulting in dehumidification.

Spray washers are used to take out some of the dirt particles in the air, and the water pressure is usually between 200 and 300kPa, with the air velocity ranging from 2 to 2.5 m/s. To keep them clean and bacteria-free, these washers need to be regularly cleaned and treated, and their water quality must be supervised and recorded. Due to the numerous cases of Legionnaires’ disease caused by air conditioning systems, the Health and Safety Executive has singled out spray washers as a potential danger to health.

Modern air-processing systems may incorporate steam injection humidifiers, but these shouldn’t be positioned right after the cooling coil. At this point, the air will likely be near the point of saturation (100% RH) and unable to absorb any more moisture. Thus, it’s better to inject the super-heated, dry steam at over 200°C into the air close to its final release.

Humudifier Applications

Humidifiers are used in a variety of applications, including residential and commercial settings, such as homes, offices, hospitals, schools, and factories. In residential settings, humidifiers are used to improve air quality, provide relief from dry air, and reduce static electricity. In commercial settings, they are used to maintain optimal levels of humidity for workers, products, and processes. Humidifiers can also be used in industrial settings to prevent corrosion and improve productivity.

Types of HVAC Humidifiers

There are two primary types of HVAC humidifiers: evaporative and steam. Evaporative humidifiers use a wick and fan system to absorb water from a reservoir, and then blow it into the air. Steam humidifiers use an electric heating element to boil water and then blow the resulting steam into the air. Both types of humidifiers have their own benefits and drawbacks, so it is important to consider the particular needs of the space before selecting an appropriate humidifier.

Humidifier Types Comparison

TypeOperating PrincipleMoisture OutputEnergy EfficiencyMaintenance RequirementsInitial CostOperating Cost
Bypass FlowUses HVAC system airflow through water panel3-11 gallons/dayHighMedium (panel replacement)LowLow
Fan-PoweredIntegrated fan pushes air through water panel6-18 gallons/dayMediumMedium (panel replacement)MediumMedium
SteamElectrically boils water to create steam13-35 gallons/dayLowLow-MediumHighHigh
UltrasonicHigh-frequency vibrations create water droplets1-4 gallons/dayVery HighHigh (cleaning)Medium-HighVery Low
Spray/AtomizingPressurized nozzles create fine water mist5-100+ gallons/dayHighHigh (nozzle maintenance)HighLow-Medium
Evaporative PadWater drips through media as air passes3-12 gallons/dayMedium-HighMedium-High (pad replacement)Low-MediumLow
Electrode CanisterElectrical current between electrodes boils water5-30 gallons/dayLowHigh (canister replacement)MediumHigh


HVAC Humidifier Selection and Sizing

The selection of the correct humidifier for an HVAC system depends on a variety of factors, including the size of the building, the climate, the amount of humidity desired, and the type of HVAC system. Each type of humidifier has its own advantages and disadvantages. In some cases, the installation of multiple types of humidifiers may be necessary to achieve the desired humidity level.

Humidity Control Parameters by Application

ApplicationRecommended RH RangeCritical Control PointsMonitoring RequirementsCommon IssuesRecommended Humidifier Type
Data Centers40-60%±5% RHContinuous with alertingElectrostatic discharge, equipment failureSteam, Ultrasonic
Healthcare Facilities30-60%±3% RHContinuous with loggingBacterial growth, patient comfortSteam (isothermal)
Residential30-50%±10% RHBasic controllerWindow condensation, comfortBypass, Fan-Powered
Museums/Archives45-55%±2% RHContinuous with loggingMaterial degradationSteam, Ultrasonic
Manufacturing40-60%Application-specificProcess integrationProduct quality, static dischargeSpray, Steam
Printing Facilities50-60%±3% RHContinuousPaper wrinkling, misalignmentSpray, Steam
Wood Processing40-55%±5% RHRegularMaterial warping, crackingSpray, Evaporative
Laboratories45-55%±2% RHContinuous with alertingTest reliability, equipment accuracySteam, Ultrasonic

Once the appropriate type of humidifier has been selected, it is important to ensure that the size of the humidifier is appropriate for the size of the building. Generally, a larger humidifier is recommended for larger buildings, as it will be able to provide more humidity to the air. However, it is possible to use a smaller humidifier in a larger building if the humidity level needs to be kept at a lower level. It is important to consult a professional to ensure the correct size is selected.

The following steps should be taken to ensure proper sizing when selecting a humidifier for an HVAC system:

1. Determine the air flow rate of the system.
2. Calculate the desired humidity level.
3. Calculate the total humidity requirement.
4. Determine the air velocity over the humidifier.
5. Select the appropriate humidifier size based on the total humidity requirement.
6. Calculate the humidifier’s energy consumption.
7. Select a humidifier that is capable of meeting the energy requirements.
8. Consider any additional features needed for the system.

Humidifier Sizing Factors

Building TypeMoisture Load FactorsCalculation VariablesTypical Capacity (lbs/hr per 1000 ft²)Air Changes Consideration
ResidentialOccupants, cooking, bathing, infiltrationVolume, construction type, occupants0.5-20.5-1 ACH
Commercial OfficeOccupants, equipment, infiltrationFloor area, occupant density, ventilation rate1-31-2 ACH
HospitalOccupants, medical equipment, ventilationDepartment type, bed count, ventilation rate3-86-15 ACH
MuseumMaterial preservation, visitorsCollection type, volume, building envelope2-51-4 ACH
IndustrialProcess requirements, air exchangesProcess type, equipment loads, exhaust rates5-20+2-60 ACH
Data CenterEquipment cooling, ventilationIT load, cooling approach, ventilation strategy1-41-4 ACH

 Water Quality Requirements by Humidifier Type

Humidifier TypeRecommended Water TypeTDS Tolerance (ppm)Hardness Tolerance (gpg)Filtration RequirementsMaintenance Impact of Poor Water Quality
Steam (Electrode)Tap water125-12503-12Basic filtrationShortened canister life, reduced output
Steam (Resistive)Treated/DI water<50<1RO or DI systemElement scaling, reduced output
UltrasonicDemineralized<5<0.5RO or DI systemWhite dust, clogged transducers
EvaporativeTap water<400<10Basic filtrationMedia scaling, reduced efficiency
Atomizing/SprayTreated water<100<3Multi-stage filtrationNozzle clogging, mineral deposits
CentrifugalTreated water<200<5Basic filtrationImpeller scaling, reduced output

Energy Consumption Comparison

Humidifier TypeCapacity Range (lbs/hr)Energy Input (kW) per lb/hrAnnual Energy Cost*Payback Period vs. Electrode SteamCO₂ Emissions (kg/yr)**
Electrode Steam5-3000.33-0.35$$$$Baseline2,800-3,000
Resistive Steam2-2500.31-0.33$$$$3-5 years2,600-2,800
Gas-Fired Steam50-30000.12-0.15$$1-3 years1,800-2,200
Ultrasonic2-400.02-0.04$1-2 years170-340
High-Pressure Atomization10-12000.005-0.02$1-3 years40-170
Evaporative5-5000.01-0.03$2-4 years85-255

*Based on 2,500 operating hours/year and average utility rates of $0.15/kWh and $0.80/therm
**Based on 0.85 kg CO₂/kWh for electricity and 0.2 kg CO₂/kWh equivalent for natural gas

Humidifier Control Integration

Control TypeAccuracyResponse TimeIntegration ComplexityCompatible SystemsTypical Applications
On/Off±10% RHSlowLowBasic HVACResidential, Small Office
Proportional±5% RHMediumMediumBMS, DDCCommercial, Light Industrial
PID±2% RHFastHighBMS, DDC, PLCCritical Environments, Healthcare
BACnet/Modbus±2-5% RHFastMedium-HighModern BMSCommercial, Institutional
IoT-Enabled±3-8% RHMedium-FastMediumCloud SystemsSmart Buildings, Remote Monitoring
Dew Point Control±1-3% RHFastHighAdvanced BMSCritical Manufacturing, Labs

Legionella Risk and Prevention by Humidifier Type

Humidifier TypeInherent Risk LevelWater Temperature RangeRequired Prevention MeasuresMaintenance FrequencyRecommended Treatments
SteamVery Low>100°CStandard water treatmentQuarterlyPeriodic draining
UltrasonicMedium-High10-30°CRegular disinfection, water treatmentWeekly-MonthlyUV, Silver ion, Biocides
Spray/AtomizingHigh10-30°CContinuous treatment, regular cleaningWeeklyUV, Chemical biocides, Regular draining
EvaporativeMedium10-35°CRegular media replacement, water treatmentMonthlyBiocides, Regular draining
Air WasherVery High15-35°CComprehensive water management planWeeklyChemical biocides, UV, Regular cleaning

Global Humidifier Manufacturers Comparison

ManufacturerSpecializationTechnology FocusMarket SegmentGeographic PresenceNotable Features
CondairComprehensiveAll technologiesAll segmentsGlobalIntegrated controllers, energy optimization
CarelControl systemsElectronic steam, adiabaticCommercial, IndustrialGlobalBMS integration, IoT connectivity
NortecSteam systemsElectrode, resistive steamCommercial, HealthcareNorth America, EuropeHygiene-certified models
DriSteemSteam systemsGas-fired, electricInstitutional, IndustrialNorth America, EuropeHigh-capacity systems
ArmstrongIndustrial systemsDirect steam injectionIndustrialGlobalProcess integration
NeptronicElectronic controlSteam, evaporativeCommercial, IndustrialNorth America, EuropeBACnet/Modbus native
HoneywellResidentialBypass, fan-poweredResidentialGlobalSmart home integration
AprilaireResidentialBypass, steamResidential, Light CommercialNorth AmericaIAQ system integration
StulzData centersAdiabatic, ultrasonicIT, Precision coolingGlobalEnergy-efficient designs
MuntersDesiccant systemsEvaporative, sprayIndustrialGlobalProcess-specific solutions